In state of the art semiconductor wafer processing systems, the wafers are processed one at a time according to a predetermined sequence of steps. For maximum efficiency in performing a particular sequence of process steps, it is preferable to perform each step in a separate, evacuatable chamber, with the multiple chambers arranged in a circular array and interconnected to one or more central transfer chambers or arranged in-line and interconnected via an in-line conveyor. This approach requires precision transfer of single wafers to and from, or along, the desired sequence of processing chambers.
To facilitate precise alignment of the wafers during transfer and to minimize the possibility of wafer breakage, it is highly desirable to move the wafers in horizontal disposition. Nevertheless, it is also preferable to process the wafers while disposed vertically. Vertical processing significantly reduces the possibility of undesired particulate contamination of the wafers, a condition to which semiconductor wafers are highly susceptible. Therefore, in processing of wafers one at a time, it is desirable to move a wafer from horizontal to vertical for performance of a processing step, and then back to horizontal, for subsequent conveyance to the next processing chamber.
Another concern in processing of semiconductor wafers relates to production efficiency. Particularly when wafers are processed one at a time, it is important to maintain maximum wafer throughput during operation of the system. This means that the time duration of the wafers in each of the chambers should be kept as short as possible, thereby to minimize overall processing time. The fewer the number of mechanical devices required to handle a wafer in any given module, the less overall time will be required to process a wafer through that particular module.
It is also important for the system to be capable of operating substantially continuously, or at least with minimum downtime for maintenance of the modules or for any intermediate steps that may occasionally be required when processing a batch of wafers. One such intermediate step is required for sputter coating, where it is necessary to preclean the sputtering target prior to coating of a new batch of wafers from a cassette. Typically, this precleaning step is accomplished by sputtering the target for a short duration. To minimize coating of surfaces within the module during precleaning, many sputtering modules include a shutter which is moved in front of the target prior to precleaning and away from the target after precleaning. This required movement of the shutter represents two mechanical steps to be performed, and as a result, wafer processing time within the sputtering module is increased and through-put for the entire system is reduced. If the shutter were to be eliminated entirely, the sputtering module would have to be cleaned more frequently, which would also result in extra downtime. In short, present methods of precleaning a sputter target decrease the overall efficiency of wafer processing.
It is an object of this invention to simply and efficiently move semiconductor wafers one at a time from a horizontal conveying disposition to a vertical processing disposition within a wafer processing module.
It is another object of this invention to reduce the number of operational steps typically associated with sputter coating a batch of semiconductor wafers.
It is still another object of the invention to increase the efficiency of operation of a sputter coating module incorporated into a wafer processing system.